Fuel efficiency of internal combustion engines can be substantially improved by varying the displacement of the engine. This allows for the full torque to be available when required, yet can significantly reduce pumping losses and improve thermal efficiency by using a smaller displacement when full torque is not required. The most common method today of implementing a variable displacement engine is to deactivate a group of cylinders substantially simultaneously.
In this approach the intake and exhaust valves associated with the deactivated cylinders are kept closed and no fuel is injected when it is desired to bypass a combustion event. For example, a 6 cylinder variable displacement engine may deactivate half of the cylinders (i.e. 3 cylinders) so that it is operating using only the remaining 3 cylinders. Commercially available variable displacement engines typically support only two or at most three displacements.
An alternative engine control approach that varies the effective displacement of an engine is referred to as “skip fire” engine control or active fuel management (AFM). In general, skip fire engine control contemplates selectively skipping the firing of certain cylinders during selected firing opportunities. Thus, a particular cylinder may be fired during one engine cycle and then may be deactivated during the next engine cycle and then selectively deactivated or fired during the next. In this manner, even finer control of the effective engine displacement is possible.
In order to deactivate a cylinder, the intake valve is prevented from opening after the power stroke by an oil control valve system and after the exhaust gas charge is discharged from the cylinder. Following the power stroke, the oil control valve system operates to prevent the exhaust valve from opening.
When more power is called for, the intake valve is reactivated by the oil control valve system and a new intake charge is drawn into the cylinder. The exhaust valve is likewise reactivated by the oil control valve system and normal engine operation is resumed.
Alternately, the exhaust valve may be deactivated first. In this alternative embodiment, to deactivate a cylinder, the exhaust valve is prevented from opening after the power stroke by an oil control valve system and the exhaust gas charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the oil control valve system operates to prevent the intake valve from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring, i.e., high pressure exhaust gas spring (HPES). As multiple cylinders are shut off at a time, the power required for compression of the exhaust gas in one cylinder is countered by the decompression of retained exhaust gas in another.
Again in this alternative embodiment, when more power is called for, the exhaust valve is reactivated first by the oil control valve system and the old exhaust gas is expelled during the exhaust stroke. The intake valve is likewise reactivated by the oil control valve system and normal engine operation is resumed.
As described, it is appreciated that accurate response timing of an oil control valve system is essential to the proper operation of active fuel management vehicles. However, current engine systems do not include a means to accurately detect and/or calibrate the time it takes for an oil valve control system to respond after a command is given to deactivate/reactivate the intake and exhaust valves of an engine cylinder. As such, it is desirable to have a method for detecting and calibrating the actuation response time for an oil control valve system of an active fuel management engine.
Furthermore, other desirable features and characteristics of the present exemplary embodiment will become apparent from the subsequent detailed description of the embodiment and the appended claims, taken in conjunction with the accompanying drawings and this background.